The Patient Core will perform the diagnosis and classification of patients who will serve as material for the studies in Project 1 (Terhorst), Project 2 (Dr. Geha) and Project 3 (Dr. Alt) and will prepare B cell lines, T cell lines and fibroblasts from patients with X-linked hyper IgM syndrome (HIGMX-1), X-linked agammaglobulinemia (XLA), autosomal recessive severe combined immunodeficiency (SCID), patients with defective TCR/CD3 expression and patients with the Hyper IgE syndrome. The Patient Core will also generate the necessary antibodies against CD40 ligand and atk/bpk for the patient studies of Alt and Geha and will identify carriers and make intrauterine diagnoses in families with HIGMX-1, XLA, and SCID. The FACS core will examine CD40 ligand (CD40L) expression in the thymus and in young children and will assess Cd40L expression in Transient Hypogammaglobulinemia of Infancy (THI), a disease with a delay in isotype switching. The FACS core will analyze lymphocytes from patients with HIGMX-1, XLA, SCID and THI and will perform all the phenotypic analyses of lymphocytes from knockout and transgenic mice generated in all 3 projects of C. Terhorst, R. Geha and F. Alt.